High speed data connections over telecommunications transmission lines such as existing telephone lines is an important technology. In particular, various kinds of DSL, such as e.g ADSL and VDSL2 are in, or are expected to come into widespread use to supply high speed data to customer premises such as homes and businesses.
DSL communications are sensitive to noise interference. In particular, impulse noise can be a problem. Impulse noise occurs as a burst or repeated bursts of very strong noise, and it can severely disrupt the reliability of the DSL connection. Impulse noise may be produced by various household electrical equipment present at customer premises (either when faulty or as a part of normal operation).
Trellis coding is a way to protect the data stream against noise interference. It works well for background noise, but is not efficient against impulse noise.
Reed-Solomon codes with interleaving is another noise protection scheme, which may be used against impulse noise. However, since impulse noise bursts are strong but relatively rare events, it is not very efficient in terms of use of memory and bandwidth. Coding and interleave must be configured for worst case noise impulses, and so most of the time, the bandwidth and memory resources allocated for noise protection aren't really needed.
A recent development of the VDSL2 standard is the inclusion of physical layer retransmission, which is described in “Draft Recommendation ITU-T G.998.4 Improved Impulse Noise Protection (INP) for DSL Transceivers”. Such retransmission is particularly useful for protection against impulse noise, as it uses bandwidth only when the transmission of a data unit was actually affected.
Several methods for impulse noise protection are described in the publication “Impulse Noise Protection Initiatives in VDSL2 Systems” by Rahul Garg, Sunita Meena, Hemant Samdani and Patrick Duvaut of Conexant Systems Inc.; in U.S. Pat. No. 7,443,916 B2 (Sedarat et. al) as well as
“Impulse noise protection for multicarrier communication systems”, Hossein Sedarat, Benjamin Miller, and Kevin Fisher, 2005 IEEE International Conference on Acoustics, Speech, and Signal Processing
As with any electronics equipment and methods for use therein, there is always a desire for improvements such as reduced memory usage and increased performance. A problem is thus to find improved ways of impulse noise protection.